fast_chr() {
	local __octal
	local __char
	printf -v __octal '%03o' $1
	printf -v __char \\$__octal
	REPLY=$__char
}

function unichr {
	local c=$1   # Ordinal of char
	local l=0    # Byte ctr
	local o=63   # Ceiling
	local p=128  # Accum. bits
	local s=''   # Output string

	(( c < 0x80 )) && { fast_chr "$c"; echo -n "$REPLY"; return; }

	while (( c > o )); do
		fast_chr $(( t = 0x80 | c & 0x3f ))
		s="$REPLY$s"
		(( c >>= 6, l++, p += o+1, o>>=1 ))
	done

	fast_chr $(( t = p | c ))
	echo -n "$REPLY$s"
}

## test harness
for (( i=0x2500; i<0x2600; i++ )); do
	unichr $i
done
